Method of preparing intermediates for retroviral protease inhibitors

ABSTRACT

A synthesis is described for intermediates which are readily amenable to the large scale preparation of hydroxyethylurea-based chiral HIV protease inhibitors. The method includes forming a diastereoselective epoxide or cyanohydrin from a chiral alpha amino aldehyde.

This application is a continuation of application Ser. No. 08/452,187;filed May 25, 1995, which was a divisional of application Ser. No.08/156,498 filed Nov. 23, 1993, which is a continuation-in-part ofapplication Ser. No. PCT/US93/04804, filed May 20, 1993, which is acontinuation-in-part of application Ser. No., 07/886,558, filed May 20,1992, which is a continuation-in-part of application Ser. No.07/789,646, filed Nov. 14, 1991, which is a continuation-in-part ofapplication Ser. No. 07/615,210, filed Nov. 19, 1990.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Synthesis of many HIV protease inhibitors containing a hydroxyethylamineor hydroxyethylurea isostere include the amine opening of a keyintermediate chiral epoxide. The synthesis of the key chiral epoxiderequires a multi-step synthesis starting from L-phenylalanine andresults in a low overall yield. The diastereoselectivity of thereduction step of the intermediate amino chloromethylketone is low anduse of explosive diazomethane prevents the scale up of the method tomultikilogram productions. The present invention relates to a method ofpreparing retroviral protease inhibitors and more particularly to adiastereoselective method of forming chiral intermediates for thepreparation of urea containing hydroxyethylamine protease inhibitors.

2. Related Art

Roberts et al, Science, 248, 358 (1990), Krohn et al, J. Med. Chem. 344,3340 (1991) and Getman, et al, J. Med. Chem., 346, 288 (1993) havepreviously reported synthesis of protease inhibitors containing thehydroxyethylamine or hydroxyethylurea isostere which include the openingof an epoxide generated in a multi-step synthesis starting from an aminoacid. These methods also contain steps which include diazomethane andthe reduction of an amino chloromethyl ketone intermediate to an aminoalcohol prior to formation of the epoxide. The overall yield of thesesyntheses are low and the use of explosive diazomethane additionallyprevents such methods from being commercially acceptable.

Tinker et al U.S. Pat. No. 4,268,688 discloses a catalytic process forthe asymmetric hydroformylation to prepare optically active aldehydesfrom unsaturated olefins. Similarly, Reetz et al U.S. Pat. No. 4,990,669discloses the formation of optically active alpha amino aldehydesthrough the reduction of alpha amino carboxylic acids or their esterswith lithium aluminum hydride followed by oxidation of the resultingprotected beta amino alcohol by dimethyl sulfoxide/oxalyl chloride orchromium trioxide/pyridine. Alternatively, protected alpha aminocarboxylic acids or esters thereof can be reduced withdiisobutylaluminum hydride to form the protected amino aldehydes.

Reetz et al (Tet. Lett., 30, 5425 (1989) disclosed the use of sulfoniumand arsonium ylides and their reactions of protected α-amino aldehydesto form aminoalkyl epoxides. This method suffers from the use of highlytoxic arsonium compounds or the use of combination of sodium hydride anddimethyl sulfoxide which is extremely hazardous in large scale. (Sodiumhydride and DMSO are incompatible: Sax, N.I., "Dangerous Properties ofIndustrial Materials", 6th Ed., Van Nostrand Reinhold Co., 1984, p. 433.Violent explosions have been reported on the reaction of sodium hydrideand excess DMSO, "Handbook of Reactive Chemical Hazards", 3rd Ed.,Butterworths, 1985, p. 295. Matteson et al Synlett., 1991, 631 reportedthe addition of chloromethylithium or bromomethylithium to racemicaldehydes.

SUMMARY OF THE INVENTION

Human immunodeficiency virus (HIV), the causative agent of acquiredimmunodeficiency syndrome (AIDS), encodes three enzymes, including thewell-characterized proteinase belonging to the aspartic proteinasefamily, the HIV protease. Inhibition of this enzyme is regarded as apromising approach for treating AIDS. One potential strategy forinhibitor design involves the introduction of hydroxyethylenetransition-state analogs into inhibitors. Inhibitors adapting thehydroxyethylamine or hydroxyethylurea isostere are found to be highlypotent inhibitors of HIV proteases. Despite the potential clinicalimportance of these compounds, previously there were no satisfactorysynthesis which could be readily and safely scaled up to prepare largekilogram quantities of such inhibitors needed for development andclinical studies. This invention provides an efficient synthesis ofintermediates which are readily amenable to the large scale preparationof hydroxyethylurea-based chiral HIV protease inhibitors.

Specifically, the method includes preparing a chiral diaminopropanolfrom a chiral alpha amino aldehyde via a diastereoselective epoxide or astereospecific cyanohydrin.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a method of preparation of HIV proteaseinhibitor that allows the preparation of commercial quantities ofintermediates of the formula ##STR1## wherein R¹ is selected from alkyl,aryl, cycloalkyl, cycloalkylalkyl and arylalkyl, which are optionallysubstituted with a group selected from alkyl, halogen, NO₂, OR⁹ or SR⁹,where R⁹ represents hydrogen or alkyl; and

R³ represents hydrogen, alkyl, alkenyl, alkynyl, hydroxyalkyl,alkoxyalkyl, cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heteroaryl,heterocycloalkylalkyl, aryl, aralkyl, heteroaralkyl, aminoalkyl andmono- and disubstituted aminoalkyl radicals, wherein said substituentsare selected from alkyl, aryl, aralkyl, cycloalkyl, cycloalkylalkyl,heteroaryl, heteroaralkyl, heterocycloalkyl, and heterocycloalkylalkylradicals, or in the case of a disubstituted aminoalkyl radical, saidsubstituents along with the nitrogen atom to which they are attached,form a heterocycloalkyl or a heteroaryl radical. Preferably, R³represents radicals as defined above which contain no alpha-branching,e.g., as in an isopropyl radical or a t-butyl radical. The preferredradicals are those which contain a --CH₂ -- moiety between the nitrogenand the remaining portion of the radical. Such preferred groups include,but are not limited to, benzyl, isobutyl, n-butyl, isoamyl,cyclohexylmethyl and the like.

P¹ and P² independently are selected from amine protecting groups,including but not limited to, arylalkyl, substituted arylalkyl,cycloalkenylalkyl and substituted cycloalkenylalkyl, allyl, substitutedallyl, acyl, alkoxycarbonyl, aralkoxycarbonyl and silyl. Examples ofarylalkyl include, but are not limited to benzyl, ortho-methylbenzyl,trityl and benzhydryl, which can be optionally substituted with halogen,alkyl of C₁ -C₈, alkoxy, hydroxy, nitro, alkylene, amino, alkylamino,acylamino and acyl, or their salts, such as phosphonium and ammoniumsalts. Examples of aryl groups include phenyl, naphthalenyl, indanyl,anthracenyl, durenyl, 9-(9-phenylfluorenyl) and phenanthrenyl,cycloalkenylalkyl or substituted cycloalkylenylalkyl radicals containingcycloalkyls of C₆ -C₁₀. Suitable acyl groups include carbobenzoxy,t-butoxycarbonyl, iso-butoxycarbonyl, benzoyl, substituted benzoyl suchas 2-methylbenzoyl, 2,6-dimethylbenzoyl 2,4,6-trimethylbenzoyl and2,4,6-triisopropylbenzoyl, 1-naphthoyl, 2-naphthoyl butyryl, acetyl,tri-fluoroacetyl, tri-chloroacetyl, phthaloyl and the like.

Additionally, the P¹ and/or P² protecting groups can form a heterocyclicring with the nitrogen to which they are attached, for example,1,2-bis(methylene)benzene, phthalimidyl, succinimidyl, maleimidyl andthe like and where these heterocyclic groups can further includeadjoining aryl and cycloalkyl rings. In addition, the heterocyclicgroups can be mono-, di- or tri-substituted, e.g., nitrophthalimidyl.The term silyl refers to a sil-con atom optionally substituted by one ormore alkyl, aryl and aralkyl groups.

Suitable carbamate protecting groups include, but are not limited to,methyl and ethyl carbamate; 9-fluorenylmethyl carbamate;9-(2-Sulfo)fluorenylmethyl carbamate; 9-(2,7-dibromo)fluorenylmethylcarbamate; 2,7-di-t-butyl-9-(10,10-dioxo-10,10,10-tetrahydrothioxanthyl)methyl carbamate;4-methoxyphenacyl carbamate; 2,2,2-trichloroethyl carbamate;2-trimethylsilylethyl carbamate; 2-phenylethyl carbamate;1-(1-adamantyl)-1-methylethyl carbamate; 1,f-dimethyl-2-haloethylcarbamate; 1,1-dimethyl-2,2-dibromoethyl carbamate;1,1-dimethyl-2,2,2-trichloroethyl carbamate;1-methyl-1-(4-biphenylyl)-ethyl carbamate;1-(3,5-di-t-butylphenyl)-1-methylethyl carbamate; 2-(2'-and4'-pyridyl)ethyl carbamate; 2-(N,N-dicyclohexylcarboxamido)ethylcarbamate; t-butyl carbamate; 1-adamantyl carbamate; vinyl carbamate;allyl carbamate; 1-isopropylallyl carbamate; cinnamyl carbamate;4-nitrocinnamyl carbamate; 8-quinolyl carbamate; N-hydroxypiperidinylcarbamate; alkyldithio carbamate; benzyl carbamate; p-methoxybenzylcarbamate; p-nitrobenzyl carbamate; p-bromobenzyl carbamate;p-chlorobenzyl carbamate; 2,4-dichlorobenzyl carbamate;4-methylsulfinylbenzyl carbamate; 9-anthrylmethyl carbamate;diphenylmethyl carbamate; 2-methylthioethyl carbamate;2-methylsulfonylethyl carbamate; 2-(p-toluenesulfonyl)ethyl carbamate;2-(1,3-dithianyl)methyl carbamate;4-methylthiophenyl-2,4-dimethylthiophenyl, 2-phosphonioethyl carbamate;2-triphenylphosphonioisopropyl carbamate; 1,1-dimethyl-2-cyanoethylcarbamate; m-chloro-p-acyloxybenzyl carbamate; p-(dihydroxyboryl)benzylcarbamate; 5-benziosoxazolylmethyl carbamate;2-(trifluoromethyl)-6-chromonylmethyl carbamate; m-nitrophenylcarbamate; 3,5-dimethoxybenzyl carbamate; o-nitrobenzyl carbamate;3,4-dimethoxy-1-nitrobenzyl carbamate; phenyl(o-nitrophenyl)methylcarbamate; phenothiazinyl-(10)-carbonyl derivative;N'-p-toluenesulfonylaminocarbonyl derivative; N'-phenylaminothiocarbonylderivative t-amyl carbamate; S-benzyl thiocarbamate; p-cyanobenzylcarbamate; cyclobutyl carbamate; cyclohexyl carbamate; cyclopentylcarbamate; cyclopropylmethyl carbamate; p-decyloxybenzyl carbamate;diisopropylmethyl carbamate; 2,2-dimethoxycarbonylvinyl carbamate;o-(N,N-dimethylcarboxamido)benzyl carbamate;1,1-dimethyl-3-(N,N-dimethylcarboxamido)propyl carbamate;1,1-dimethylpropynyl carbamate; di(2-pyridyl)methyl carbamate;2-furanylmethyl carbamate; 2-iodoethyl carbamate; isobornyl carbamate;isobutyl carbamate; isonicotinyl carbamate;p-(p'-methoxyphenylazo)benzyl carbamate; 1-methylcyclobutyl carbamate;1-methylcyclohexyl carbamate; 1-methyl-1-cyclopropylmethyl carbamate;1-methyl-1-(3,5-dimethoxyphenyl)ethyl carbamate;1-methyl-1-(p-phenylazophenyl)ethyl carbamate; and1-methyl-1-phenylethyl carbamate. T. Greene and P. Wuts ("ProtectiveGroups In Organic Synthesis," 2nd Ed., John Wiley & Sons, Inc. (1991))describe the preparation and cleavage of such carbamate protectinggroups.

Suitable silyl protecting groups include, but are not limited to,trimethylsilyl, triethylsilyl, tri-isopropylsilyl,tert-butyldimethylsilyl, dimethylphenylsilyl,1,2-bis(dimethylsilyl)benzene, 1,2-bis(dimethylsilyl)ethane anddiphenylmethylsilyl. Silylation of the amine functions to provide mono-or bis-disilylamine can provide derivatives of the aminoalcohol, aminoacid, amino acid esters and amino acid amide. In the case of aminoacids, amino acid esters and amino acid amides, reduction of thecarbonyl function provides the required mono- or bis-silyl aminoalcohol.Silylation of the aminoalcohol can lead to the N,N,O-tri-silylderivative. Removal of the silyl function from the silyl ether functionis readily accomplished by treatment with, for example, a metalhydroxide or ammonium flouride reagent, either as a discrete reactionstep or in situ during the preparation of the amino aldehyde reagent.Suitable silylating agents are, for example, trimethylsilyl chloride,tert-buty-dimethylsilyl chloride, phenyldimethylsilyl chlorie,diphenylmethylsilyl chloride or their combination products withimidazole or DMF. Methods for silylation of amines and removal of silylprotecting groups are well known to those skilled in the art. Methods ofpreparation of these amine derivatives from corresponding amino acids,amino acid amides or amino acid esters are also well known to thoseskilled in the art of organic chemistry including amino acid/amino acidester or aminoalcohol chemistry.

Preferably P¹ is selected from aralkyl, substituted aralkyl,alkylcarbonyl, aralkylcarbonyl, arylcarbonyl, alkoxycarbonyl andaralkoxycarbonyl, P² is selected from aralkyl and substituted aralkyland R¹ is selected from aralkyl and substituted aralkyl. Alternatively,when P¹ is alkoxycarbonyl or aralkoxycarbonyl, P² can be hydrogen. Morepreferably, P¹ is t-butoxycarbonyl, phenylmethoxycarbonyl or benzyl, P²is hydrogen or benzyl and R¹ is benzyl.

Protected amino epoxides of the formula ##STR2## protected aminoalpha-hydroxycyanides and acids of the formula ##STR3## wherein X is--CN, --CH₂ NO₂ or --COOH, protected alpha-aminoaldehyde intermediatesof the formula ##STR4## and protected chiral alpha-amino alcohols of theformula ##STR5## wherein P¹, P² and R¹ are as defined above, are alsodescribed herein.

As utilized herein, the term "amino epoxide" alone or in combination,means an amino-substituted alkyl epoxide wherein the amino group can bea primary, or secondary amino group containing substituents selectedfrom hydrogen, and alkyl, aryl, aralkyl, alkenyl, alkoxycarbonyl,aralkoxycarbonyl, cycloalkenyl, silyl, cycloalkylalkenyl radicals andthe like and the epoxide can be alpha to the amine. The term "aminoaldehyde" alone or in combination, means an amino-substituted alkylaldehyde wherein the amino group can be a primary, or secondary aminogroup containing substituents selected from hydrogen, and alkyl, aryl,aralkyl, alkenyl, aralkoxycarbonyl, alkoxycarbonyl, cycloalkenyl, silyl,cycloalkylalkenyl radicals and the like and the aldehyde can be alpha tothe amine. The term "alkyl", alone or in combination, means astraight-chain or branched-chain alkyl radical containing from 1 toabout 10, preferably from 1 to about 8, carbon atoms. Examples of suchradicals include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl,sec-butyl, tert-butyl, pentyl, iso-amyl, hexyl, octyl and the like. Theterm "alkenyl", alone or in combination, means a straight-chain orbranched-chain hydrocarbon radial having one or more double bonds andcontaining from 2 to about 18 carbon atoms preferably from 2 to about 8carbon atoms. Examples of suitable alkenyl radicals include ethenyl,propenyl, allyl, 1,4-butadienyl and the like. The term "alkoxy", aloneor in combination, means an alkyl ether radical wherein the term alkylis as defined above. Examples of suitable alkyl ether radicals includemethoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, iso-butoxy,sec-butoxy, tert-butoxy and the like. The term "cycloalkenyl", alone orin combination, means an alkyl radical which contains from about 3 toabout 8 carbon atoms and is cyclic and which contains at least onedouble bond in the ring which is non-aromatic in character. The term"alkynyl", alone or in combination, means a straight-chain hydrocarbonradical having one or more triple bonds and containing from 2 to about10 carbon atoms. Examples of alkynyl radicals include ethynyl, propynyl,(propargyl), butynyl and the like. The term "cycloalkenylalkyl" meanscycloalkenyl radical as defined above which is attached to an alkylradical, the cyclic portion containing from 3 to about 8, preferablyfrom 3 to about 6, carbon atoms. Examples of such cycloalkenyl radicalsinclude cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl,dihydrophenyl and the like. ₋₋₋₋ The term "cycloalkyl", alone or incombination, means an alkyl radical which contains from about 3 to about8 carbon atoms and is cyclic. The term "cycloalkylalkyl" means an alkylradical as defined above which is substituted by a cycloalkyl radicalcontaining from about 3 to about 8, preferably from about 3 to about 6,carbon atoms. Examples of such cycloalkyl radicals include cyclopropyl,cyclobutyl, cyclopentyl, cyclohexyl and the like. The term "aryl", aloneor in combination, means a carbocyclic aromatic system containing one,two or three rings wherein such rings may be attached together in apendent manner or may be fused. Examples of "aryl" include phenyl ornaphthyl radical either of which optionally carries one or moresubstituents selected from alkyl, alkoxy, halogen, hydroxy, amino, nitroand the like, as well as p-tolyl, 4-methoxyphenyl,4-(tert-butoxy)phenyl, 4-fluorophenyl, 4-chlorophenyl, 4-hydroxyphenyl,1-naphthyl, 2-naphthyl, and the like. The term "aralkyl", alone or incombination, means an alkyl radical as defined above in which onehydrogen atom is replaced by an aryl radical as defined above, such asbenzyl, 2-phenylethyl and the like. Examples of substituted aralkylinclude 3,5-dimethoxybenzyl bromide, 3,4-dimethoxybenzyl bromide,2,4-dimethoxybenzyl bromide, 3,4,5-trimethoxybenzyl bromide,4-nitrobenzyl iodide, 2,6-dichlorobenzyl bromide,1,4-bis(chloromethyl)benzene, 1,2-bis(bromomethyl)benzene,1,3-bis(chloromethyl)-benzene, 4-chlorobenzyl chloride, 3-chlorobenzylchloride, 1,2-bis(chloromethyl)benzene, 6-chloropiperonyl chloride,2-chlorobenzyl chloride, 4-chloro-2-nitrobenzyl chloride,2-chloro-6-fluorobenzyl chloride,1,2-bis(chloromethyl)-4,5-dimethylbenzene, 3,6-bis(chloromethyl)durene,9,10-bis(chloromethyl)anthracene, 2,5-bis(chloromethyl)-p-xylene,2,5-bis(chloromethyl)-1,4-dimethoxybenzene,2,4-bis(chloromethyl)anisole, 4,6-(dichloromethyl)-m-xylene,2,4-bis(chloromethyl)mesitylene,4-(bromomethyl)-3,5-dichlorobenzophenone,n-(alpha-chloro-o-tolyl)-benzylamine hydrochloride,3-(chloromethyl)benzoyl chloride, 2-chloro-4-chloromechyltoluene,3,4-dichlorobenzyl bromide, 6-chloro-8-chloromethylbenzo-1,3-dioxan,4-(2,6-dichlorobenzylsulphonyl)benzylbromide,5-(4-chloromethylphenyl)-3-(4-chlorophenyl)-1,2,4-oxadiazole,5-(3-chloromethylphenyl)-3-(4-chlorophenyl)-1,2,4-oxadiazole,4-(chloromethyl)benzoyl chloride, di(chioromethyl)toluene,4-chloro-3-nitrobenzyl chloride,1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane,1-(dimethylchlorosilyl)-2-(p,m-chloromethylphenyl)ethane,3-chloro-4-methoxybenzyl chloride, 2,6-bis(chloromethyl)-4-methylphenol,2,6-bis(chloromethyl)-p-tolyl acetate, 4-bromobenzyl bromide,p-bromobenzoyl bromide, alpha alpha'-dibromo-m-xylene, 3-bromobenzylbromide, 2-bromobenzyl bromide, 1,8-bis(bromomethyl)naphthalene,o-xylylene dibromide, p-xylylene dibromide,2,2'-bis(bromomethyl)-1,1'-biphenyl,alpha,alphal'-dibromo-2,5-dimethoxy-p-xylene, benzyl chloride, benzylbromide, 4,5-bis(bromomethyl)phenanthrene,3-(bromomethyl)benzyltriphenylphosphonium bromide,4-(bromomethyl)benzyltriphenylphosphonium bromide,2-(bromomethyl)benzyltriphenylphosphonium bromide,1-(2-bromoethyl)-2-(bromomethyl)-4-nitrobenzene,2-bromo-5-fluorobenzylbromide, 2,6-bis(bromomethyl) fluorobenzene,o-bromomethylbenzoyl bromide, p-bromomethyl benzoyl bromide,1-bromo-2-(bromomethyl)naphthalene, 2-bromo-5-methoxybenzyl bromide,2,4-dichlorobenzyl chloride, 3,4-dichlorobenzyl chloride,2,6-dichlorobenzyl chloride, 2,3-dichlorobenzyl chloride,2,5-dichlorobenzyl chloride,methyldichlorosilyl(chloromethylphenyl)ethane,methyldichlorosilyl(chloromethylphenyl)ethane,methyldichlorosilyl(chloromethylphenyl)ethane, 3,5-dichlorobenzylchloride, 3,5-dibromo-2-hydroxybenzyl bromide, 3,5-dibromobenzylbromide, p-(chloromethyl)phenyltrichlorosilane,1-trichiorosilyl-2-(p,m-chloromethylphenyl)ethane,1-trichlorosilyl-2-(p,m-chloromethylphenyl)ethane,1,2,4,5-tetrakis(bromomethyl)benzene. The term aralkoxycarbonyl means anaralkoxyl group attached to a carbonyl. Carbobenzoxy is an example ofaralkoxycarbonyl. The term "heterocyclic ring system" means a saturatedor partially unsaturated monocyclic, bicyclic or tricyclic heterocyclewhich contains one or more hetero atoms as ring atoms, selected fromnitrogen, oxygen, silicon and sulphur, which is optionally substitutedon one or more carbon atoms by halogen, alkyl, alkoxy, oxo, and thelike, and/or on a secondary nitrogen atom (i.e., --NH--) by alkyl,aralkoxycarbonyl, alkanoyl, phenyl or phenylalkyl or on a tertiarynitrogen atom (i.e. ═N--) by oxido and which is attached via a carbonatom. The heteroaryl portion of a heteroaroyl, heteroaryloxycarbonyl, ora heteroaralkoxy carbonyl group or the like is an aromatic monocyclic,bicyclic, or tricyclic heterocycle which contains the hetero atoms andis optionally substituted as defined above with respect to thedefinition of aryl. Examples of such heterocyclic groups arepyrrolidinyl, piperidinyl, piperazinyl, morpholinyl, thiamorpholinyl,pyrrolyl, phthalimide, succinimide, maleimide, and the like. Alsoincluded are heterocycles containing two silicon atoms simultaneouslyattached to the nitrogen and joined by carbon atoms. The term"alkylamino" alone or in combination, means an amino-substituted alkylgroup wherein the amino group can be a primary, or secondary amino groupcontaining substituents selected from hydrogen, and alkyl, aryl,aralkyl, cycloalkyl, cycloalkylalkyl radicals and the like. The term"halogen" means fluorine, chlorine, bromine or iodine. The termdihaloalkyl means two halogen atoms, the same or different, substitutedon the same carbon atom. The term "oxidizing agent" includes a singleagent or a mixture of oxidizing reagents. Examples of mixtures ofoxidizing reagents include sulfur trioxide-pyridine/dimethylsulfoxide,oxalyl chioride/dimethyl sulfoxide, acetyl chloride/dimethyl sulfoxide,acetyl anhydride/dimethyl sulfoxide, trifluoroacetyl chioride/dimethylsulfoxide, toluenesulfonyl bromide/dimethyl sulfoxide, phosphorouspentachloride/dimethyl sulfoxide and isobutylchloroformate/dimethylsulfoxide.

A general Scheme for the preparation of amino epoxides, useful asintermediates in the synthesis of HIV protease inhibitors is shown inScheme 1 below. ##STR6##

The economical and safe large scale method of preparation of proteaseinhibitors of the present invention can alternatively utilize aminoacids or amino alcohols to form N,N-protected alpha aminoalcohol of theformula ##STR7## wherein P¹, P² and R¹ are described above.

Whether the compounds of Formula II are formed from amino acids oraminoalcohols, such compounds have the amine protected with groups P¹and P² as previously identified. The nitrogen atom can be alkylated suchas by the addition of suitable alkylating agents in an appropriatesolvent in the presence of base.

Alternate bases used in alkylation include sodium hydroxide, sodiumbicarbonate, potassium hydroxide, lithium hydroxide, potassiumcarbonate, sodium carbonate, cesium hydroxide, magnesium hydroxide,calcium hydroxide or calcium oxide, or tertiary amine bases such astriethyl amine, diisopropylethylamine, N-methylpiperidine, pyridine,dimethylaminopyridine and azabicyclononane. Reactions can be homogenousor heterogenous. Suitable solvents are water and protic solvents orsolvents miscible with water, such as methanol, ethanol, isopropylalcohol, tetrahydrofuran and the like, with or without added water.Dipolar aprotic solvents may also be used with or without added proticsolvents including water. Examples of dipolar aprotic solvents includeacetonitrile, dimethylformamide, dimethyl acetamide, acetamide,tetramethyl urea and its cyclic analog, dimethylsulfoxide,N-methylpyrrolidone, sulfolane, nitromethane and the like. Reactiontemperature can range between about -20° to 100° C. with the preferredtemperature of about 25°-85° C. The reaction may be carried out under aninert atmosphere such as nitrogen or argon, or normal or dry air, underatmospheric pressure or in a sealed reaction vessel under positivepressure. The most preferred alkylating agents are benzyl bromide orbenzyl chloride or monosubstituted aralkyl halides or polysubstitutedaralkyl halides. Sulfate or sulfonate esters are also suitable reagentsto provide the corresponding benzyl analogs and they can be preformedfrom the corresponding benzyl alcohol or formed in situ by methods wellknown to those skilled in the art. Trityl, benzhydryl, substitutedtrityl and substituted benzhydryl groups, independently, are alsoeffective amine protecting groups P¹,P² ! as are allyl and substitutedallyl groups. Their halide derivatives can also be prepared from thecorresponding alcohols by methods well known to those skilled in the artsuch as treatment with thionyl chloride or bromide or with phosphorustri- or pentachloride, bromide or iodide or the corresponding phosphoryltrihalide. Examples of groups that can be substituted on the aryl ringinclude alkyl, alkoxy, hydroxy, nitro, halo and alkylene, amino, mono-and dialkyl amino and acyl amino, acyl and water solubilizing groupssuch as phosphonium salts and ammonium salts. The aryl ring can bederived from, for example, benzene, napthelene, indane, anthracene,9-(9-phenyl fluorenyl, durene, phenanthrene and the like. In addition,1,2-bis (substituted alkylene) aryl halides or sulfonate esters can beused to form a nitrogen containing aryl or non-aromatic heterocyclicderivative with P¹ and P² ! or bis-heterocycles. Cycloalkylenealkyl orsubstituted cyloalkylene radicals containing 6-10 carbon atoms andalkylene radicals constitute additional acceptable class of substituentson nitrogen prepared as outlined above including, for example,cyclohexylenemethylene.

Compounds of Formula II can also be prepared by reductive alkylation by,for example, compounds and intermediates formed from the addition of analdehyde with the amine and a reducing agent, reduction of a SchiffBase, carbinolamine or enamine or reduction of an acylated aminederivative. Reducing agents include metals platinum, palladium,palladium hydroxide, palladium on carbon, platinum oxide, rhodium andthe like! with hydrogen gas or hydrogen transfer molecules such ascyclohexene or cyclohexadiene or hydride agents such as lithiumaluminumhydride, sodium borohydride, lithium borohydride, sodiumcyanoborohydride, diisobutylaluminum hydride or lithiumtri-tert-butoxyaluminum hydride.

Additives such as sodium or potassium bromide, sodium or potassiumiodide can catalyze or accelerate the rate of amine alkylation,especially when benzyl chloride was used as the nitrogen alkylatingagent.

Phase transfer catalysis wherein the amine to be protected and thenitrogen alkylating agent are reacted with base in a solvent mixture inthe presence of a phase transfer reagent, catalyst or promoter. Themixture can consist of, for example, toluene, benzene, ethylenedichloride, cyclohexane, methylene chloride or the like with water or aaqueous solution of an organic water miscible solvent such as THF.Examples of phase transfer catalysts or reagents includetetrabutylammonium chloride or iodide or bromide, tetrabutylammoniumhydroxide, tri-butyloctylammonium chloride, dodecyltrihexylammoniumhydroxide, methyltrihexylammonium chloride and the like.

A preferred method of forming substituted amines involves the aqueousaddition of about 3 moles of organic halide to the amino acid or about 2moles to the aminoalcohol. In a more preferred method of forming aprotected amino alcohol, about 2 moles of benzylhalide in a basicaqueous solution is utilized. In an even more preferred method, thealkylation occurs at 50° C. to 80° C. with potassium carbonate in water,ethanol/water or denatured ethanol/water. In a more preferred method offorming a protected amino acid ester, about 3 moles of benzylhalide isadded to a solution containing the amino acid.

The protected amino acid ester is additionally reduced to the protectedamino alcohol in an organic solvent. Preferred reducing agents includelithium aluminiumhydride, lithium borohydride, sodium borohydride,borane, lithium tri-tert-butoxyaluminum hydride, borane•THF complex.Most preferably, the reducing agent is diisobutylaluminum hydride(DiBAL-H) in toluene. These reduction conditions provide an alternativeto a lithium aluminum hydride reduction.

Purification by chromatography is possible. In the preferredpurification method the alpha amino alcohol can be purified by an acidquench of the reaction, such as with hydrochloric acid, and theresulting salt can be filtered off as a solid and the amino alcohol canbe liberated such as by acid/base extraction.

The protected alpha amino alcohol is oxidized to form a chiral aminoaldehyde of the formula ##STR8## Acceptable oxidizing reagents include,for example, sulfur trioxide-pyridine complex and DMSO, oxalyl chlorideand DMSO, acetyl chloride or anhydride and DMSO, trifluoroacetylchloride or anhydride and DMSO, methanesulfonyl chloride and DMSO ortetrahydrothiaphene-S-oxide, toluenesulfonyl bromide and DMSO,trifluoromethanesulfonyl anhydride (triflic anhydride) and DMSO,phosphorus pentachloride and DMSO, dimethylphosphoryl chloride and DMSOand isobutylchloroformate and DMSO. The oxidation conditions reported byReetz et al Angew Chem., 99, p. 1186, (1987)!, Angew Chem. Int. Ed.Enal., 26, p. 1141, 1987) employed oxalyl chloride and DMSO at -78° C.

The preferred oxidation method described in this invention is sulfurtrioxide pyridine complex, triethylamine and DMSO at room temperature.This system provides excellent yields of the desired chiral protectedamino aldehyde usable without the need for purification i.e., the needto purify kilograms of intermediates by chromatography is eliminated andlarge scale operations are made less hazardous. Reaction at roomtemperature also eliminated the need for the use of low temperaturereactor which makes the process more suitable for commercial production.

The reaction may be carried out under an inert atmosphere such asnitrogen or argon, or normal or dry air, under atmospheric pressure orin a sealed reaction vessel under positive pressure. Preferred is anitrogen atmosphere. Alternative amine bases include, for example,tri-butyl amine, tri-isopropyl amine, N-methylpiperidine, N-methylmorpholine, azabicyclononane, diisopropylethylamine,2,2,6,6-tetramethylpiperidine, N,N-dimethylaminopyridine, or mixtures ofthese bases. Triethylamine is a preferred base. Alternatives to pureDMSO as solvent include mixtures of DMSO with non-protic or halogenatedsolvents such as tetrahydrofuran, ethyl acetate, toluene, xylene,dichloromethane, ethylene dichloride and the like. Dipolar aproticco-solvents include acetonitrile, dimethylformamide, dimethylacetamide,acetamide, tetramethyl urea and its cyclic analog, N-methylpyrrolidone,sulfolane and the like. Rather than N,N-dibenzylphenylalaninol as thealdehyde precursor, the phenylalaninol derivatives discussed above canbe used to provide the corresponding N-monosubstituted either P¹ or P²=H! or N,N-disubstituted aldehyde.

In addition, hydride reduction of an amide or ester derivative of thecorresponding alkyl, benzyl or cycloalkenyl nitrogen protectedphenylalanine, substituted phenylalanine or cycloalkyl analog ofphenyalanine derivative can be carried out to provide a compound ofFormula III. Hydride transfer is an additional method of aldehydesynthesis under conditions where aldehyde condensations are avoided, cf,Oppenauer Oxidation.

The aldehydes of this process can also be prepared by methods ofreducing protected phenylalanine and phenylalanine analogs or theiramide or ester derivatives by, e.g., sodium amalgam with HCl in ethanolor lithium or sodium or potassium or calcium in ammonia. The reactiontemperature may be from about -20° C. to about 45° C., and preferablyfrom abut 5° C. to about 25° C. Two additional methods of obtaining thenitrogen protected aldehyde include oxidation of the correspondingalcohol with bleach in the presence of a catalytic amount of2,2,6,6-tetramethyl-1-pyridyloxy free radical. In a second method,oxidation of the alcohol to the aldehyde is accomplished by a catalyticamount of tetrapropylammonium perruthenate in the presence ofN-methylmorpholine-N-oxide.

Alternatively, an acid chloride derivative of a protected phenylalanineor phenylalanine derivative as disclosed above can be reduced withhydrogen and a catalyst such as Pd on barium carbonate or bariumsulphate, with or without an additional catalyst moderating agent suchas sulfur or a thiol (Rosenmund Reduction).

An important aspect of the present invention is a reaction involving theaddition of chloromethylithium or bromomethyllithium to the α-aminoaldehyde. Although addition of chloromethyllithium or bromomethylithiumto aldehydes is known, the addition of such species to racemic or chiralamino aldehydes to form aminoepoxides of the formula ##STR9## is novel.The addition of chloromethylithium or bromomethylithium to a chiralamino aldehyde is highly diastereoselective. Preferably, thechloromethyllithium or bromomethylithium is generated n-situ from thereaction of the dihalomethane and n-butyllithium. Acceptablemethyleneating halomethanes include chloroiodomethane,bromochloromethane, dibromomethane, diiodomethane, bromofluoromethaneand the like. The sulfonate ester of the addition product of, forexample, hydrogen bromide to formaldehyde is also a methyleneatingagent. Tetrahydrofuran is the preferred solvent, however alternativesolvents such as toluene, dimethoxyethane, ethylene dichloride,methylene chloride can be used as pure solvents or as a mixture. Dipolaraprotic solvents such as acetonitrile, DMF, N-methylpyrrolidone areuseful as solvents or as part of a solvent mixture. The reaction can becarried out under an inert atmosphere such as nitrogen or argon. Forn-butyl lithium can be substituted other organometalic reagents reagentssuch as methyllithium, tert-butyl lithium, sec-butyl lithium,phenyllithium, phenyl sodium and the like. The reaction can be carriedout at temperatures of between about -80° C. to 0° C. but preferablybetween about -80° C. to -20° C. The most preferred reactiontemperatures are between -40° C. to -15° C. Reagents can be added singlybut multiple additions are preferred in certain conditions. Thepreferred pressure of the reaction is atmospheric however a positivepressure is valuable under certain conditions such as a high humidityenvironment.

Alternative methods of conversion to the epoxides of this inventioninclude substitution of other charged methylenation precursor speciesfollowed by their treatment with base to form the analogous anion.Examples of these species include trimethylsulfoxonium tosylate ortriflate, tetramethylammonium halide, methyldiphenylsulfoxonium halidewherein halide is chloride, bromide or iodide.

The conversion of the aldehydes of this invention into their epoxidederivative can also be carried out in multiple steps. For example, theaddition of the anion of thioanisole prepared from, for example, a butylor aryl lithium reagent, to the protected aminoaldehyde, oxidation ofthe resulting protected aminosulfide alcohol with well known oxidizingagents such as hydrogen peroxide, tert-butyl hypochlorite, bleach orsodium periodate to give a sulfoxide. Alkylation of the sulfoxide with,for example, methyl iodide or bromide, methyl tosylate, methyl mesylate,methyl triflate, ethyl bromide, isopropyl bromide, benzyl chloride orthe like, in the presence of an organic or inorganic base.Alternatively, the protected aminosulfide alcohol can be alkylated with,for example, the alkylating agents above, to provide a sulfonium saltsthat are subsequently converted into the subject epoxides withtert-amine or mineral bases.

The desired epoxides form, using most preferred conditions,diastereoselectively in ratio amounts of at least about an 85:15 ratio(S:R). The product can be purified by chromatography to give thediastereomerically and enantiomerically pure product but it is moreconveniently used directly without purification to prepare HIV proteaseinhibitors.

The epoxide is then reacted, in a suitable solvent system, with an equalamount, or preferably an excess of, with R³ NH₂ to form the aminoalcohol of Formula I ##STR10## wherein R³ is as defined above.

The reaction can be conducted over a wide range of temperatures, e.g.,from about 10° C. to about 100° C., but is preferably, but notnecessarily, conducted at a temperature at which the solvent begins toreflux. Suitable solvent systems include those wherein the solvent is analcohol, such as methanol, ethanol, isopropanol, and the like, etherssuch as tetrahydrofuran, dioxane and the like, and toluene,N,N-dimethylformamide, dimethyl sulfoxide, and mixtures thereof. Apreferred solvent is isopropanol. Exemplary amines corresponding to theformula R³ NH₂ include benzyl amine, isobutylamine, n-butyl amine,isopentyl amine, isoamylamine, cyclohexanemethyl amine, naphthylenemethyl amine and the like. In some cases, R³ NH₂ can be used as thesolvent, such as iso-butylamine.

Alternatively, the protected amino aldehyde of Formula III can also bereacted with a cyanide salt, such as sodium cyanide or potassium cyanideto form a chiral cyanohydrin of the formula ##STR11## Preferably, areaction rate enhancer, such as sodium bisulfite, is used to enhance therate of cyanohydrin formation. Alternatively, trimethylsilylnitrile canbe used to form a trimethylsilyloxycyano intermediate, which can bereadily hydrolized to the cyanohydrin.

The reaction can be carried out at temperatures of between about -5° C.to 5° C. but preferably between about 0° C. to 5° C. The desiredcyanohydrins form, using sodium cyanide and sodium bisuifite,diastereoselectively in ratio amounts of at least about an 88:12 ratio(S:R). The product can be purified bv Chromatography co give thediastereomerically and enantiomerically pure product.

The cyano group can be reduced to the amine of Formula V ##STR12## Thereduction can be accomplished using a variety of reducing reagents, suchas hydride transfer, metal reductions and catalytic hydrogenation whichare well known to those skilled in the art. Examples of hydride reagentswith and without heavy metal(s) or heavy metal salts as adjunct reagentsinclude, for example, lithium aluminum hydride, lithiumtri-tert-butoxyaluminum hydride, lithium trimethoxy-aluminum hydride,aluminum hydride, diborane (or borane), borane/THF, borane/dimethylsulfide, borane/pyridine, sodium borohydride, lithium borohydride,sodium borohydride/cobalt salts, sodium borohydride/Raney-nickel, sodiumborohydride/acetic acid and the like. Solvents for the reaction include,for the more reactive hydrides, THF, diethyl ether, dimethoxy ethane,diglyme, toluene, heptane, cyclohexane, methyl tert-butyl ether and thelike. Solvents or solvent mixtures for reductions using reagents such assodium borohydride, in addition to the non-protic solvents listed above,can include ethanol, n-butanol, tert-butyl alcohol, ethylene glycol andthe like. Metal reductions include, for example, sodium and ethanol.Reaction temperatures can vary between solvent reflux and -20° C. Aninert atmosphere such as nitrogen or argon is usually preferredespecially where the possibility of flammable gas or solventproduction/evolution is possible. Catalytic hydrogenation (metalcatalyst plus hydrogen gas) can be carried out in the same solvents asabove with metals or metal salts such a nickel, palladium chloride,platinum, rhodium, platinum oxide or palladium on carbon or othercatalysts known to those skilled in the art. These catalysts can also bemodified with, for example, phosphine ligands, sulfur or sulfurcontaining compounds or amines such as quinoline. Hydrogenations can becarried out at atmospheric pressure or at elevated pressures to about1500 psi at temperatures between 0° to about 250° C. The most preferredreducing reagent is diborane•tetrahydrofuran, preferably at roomtemperature under an atmosphere of nitrogen and atmospheric pressure.

The amine of Formula V can then be reacted with R³ L, wherein L is aleaving group selected from halo, tosylate, and the like, and R³represents alkyl, alkenyl, alkynyl, hydroxyalkyl, alkoxyalkyl,cycloalkyl, cycloalkylalkyl, heterocycloalkyl, heterocycloalkylalkyl,aralkyl, and heteroaralkyl. Alternatively, the primary amino group ofFormula V can be reductively alkylated with an aldehyde to introduce theR3 group. For example, when R3 is an isobutyl group, treatment ofFormula V with isobutyraldehyde under reductive amination conditionsaffords the desired Formula I. Similarly, when R3 is an isoamyl group,treatment of Formula V with isovaleraldehyde under reductive aminationconditions affords the desired Formula I. Other.aldehydes can be used tointroduce various R3 groups. Reductive amination can be performed usinga variety of reaction conditions well-known to those skilled in the art.For example, the reductive amination of Formula V with an aldehyde canbe carried out with a reducing agent such as sodium cyanoborohydride orsodium borohydride in a suitable solvent, such as methanol, ethanol,tetrahydrofuran and the like. Alternatively, the reductive amination canbe carried out using hydrogen in the presence of a catalyst such aspalladium or platinum, palladium on carbon or platinum on carbon, orvarious other metal catalysts known to those skilled in the art, in asuitable solvent such as methanol, ethanol, tetrahydrofuran, ethylacetate, toluene and the like.

Alternatively, the amine of Formula I can be prepared by reduction ofthe protected amino acid of formula ##STR13## (commercially availablefrom Nippon Kayaku, Japan) to the corresponding alcohol of formula##STR14## The reduction can be accomplished using a variety of reducingreagents and conditions. A preferred reducing reagent isdiborane•tetrahydrofuran. The alcohol is then converted into a leavinggroup (L') by tosylation, mesylation or conversion into a halo group,such as chloro or bromo: ##STR15## Finally, the leaving group (L') isreacted with R³ NH₂ as described above to form amino alcohol of FormulaI. Alternatively, base treatment of the alcohol can result in theformation of the amino epoxide of Formula IV.

The above preparation of amino alcohol of Formula I is applicable trmixtures of optical isomers as well as resolved compounds. If aparticular optical isomer is desired, it can be selected by the choiceof starting material, e.g., L-phenylalanine, D-phenylalanine,L-phenylalaninol, D-phenylalaninol, D-hexahydrophenylalaninol and thelike, or resolution can occur at intermediate or final steps. Chiralauxiliaries such as one or two equivalents of camphor sulfonic acid,citric acid, camphoric acid, 2-methoxyphenylacetic acid and the like canbe used to form salts, esters or amides of the compounds of thisinvention. These compounds or derivatives can be crystallized orseparated chromatographically using either a chiral or achiral column asis well known to those skilled in the art.

A further advantage of the present process is that materials can becarried through the above steps without purification of the intermedateproducts. However, if purification is desired, the intermediatesdisclosed can be prepared and stored in a pure state.

The practical and efficient synthesis described here has beensuccessfully scaled up to prepare large quantity of intermediates forthe preparation of HIV protease inhibitors. It offers several advantagesfor multikilogram preparations: (1) it does not require the use ofhazardous reagents such as diazomethane, (2) it requires no purificationby chromatography, (3) it is short and efficient, (4) it utilizesinexpensive and readily available commercial reagents, (5) it producesenantiomerically pure alpha amino epoxides. In particular, the processof the invention produces enantiomerically-pure epoxide as required forthe preparation of enantiomerically-pure intermediate for furthersynthesis of HIV protease inhibitors.

The amino epoxides were prepared utilizing the following procedure asdisclosed in Scheme II below. ##STR16## In Scheme II, there is shown asynthesis for the epoxide, chiral N,N,α-S-tris(phenylmethyl)-2S-oxiranemethan-amine. The synthesis startsfrom L-phenylalanine. The aldehyde is prepared In three steps fromL-phenylalanine or phenylalinol. L-Phenylalanine is converted to theN,N-dibenzylamino acid benzyl ester using benzyl bromide under aqueousconditions. The reduction of benzyl ester is carried out usingdiisobutylaluminum hydride (DIBAL-H) in toluene. Instead of purificationby chromatography, the product iss purified by an acid (hydrochloricacid) quench of the reaction, the hydrochloride salt is filtered off asa white solid and then liberated by an acid/base extraction. After onerecrystallization, chemically and optically pure alcohol is obtained.Alternately, and preferably, the alcohol can be obtained in one step in88% yield by the benzylation of L-phenylalaninol using benzylbromideunder aqueous conditions. The oxidation of alcohol to aldehyde is alsomodified to allow for more convenient operation during scaleup. Insteadof the standard Swern procedures using oxalyl chloride and DMSO inmethylene chloride at low temperatures (very exothermic reaction),sulfur trioxide-pyridine/DMSO was employed (Parikh, J., Doering, W., J.Am. Chem. Soc., 89, p. 5505, 1967) which can be conveniently performedat room temperature to give excellent yields of the desired aldehydewith high chemical and enantiomer purity which does not requirepurification.

An important reaction involves the addition of chloromethylithium orbromomethylithium to the aldehyde. Although addition ofchloromethyllithium or bromomethylithium to aldehydes has been reportedpreviously, the addition of such species to chiral α-amino aldehydes toform chiral-aminoepoxides is believed to be novel. Now,chioromethyllithium or bromomethylithium is generated in-situ fromchloroiodomethane(or bromochloromethane) or dibromomethane andn-butyllithium at a temperature in a range from about -78° C. to about-10° C. in THF in the presence of aldehyde. The desired chlorohydrin orbromohydrin is formed as evidenced by TLC analyses. After warming toroom temperature, the desired epoxide is formed diastereoselectively ina 85:15 ratio (S:R). The product can be purified by chromatography togive the diastereomerically pure product as a colorless oil but it ismore conveniently used directly without purification.

Scheme III illustrates the preparation of the aminopropylurea (9)utilizing mixed protected amine of phenylalaninol, where BOC ist-butoxycarbonyl and Bn is benzyl. ##STR17##

Scheme IV illustrates an alternative preparation of the amino epoxide(5) utilizing a sulfur ylide. ##STR18## The aminopropylurea (9) was alsoprepared utilizing the procedure as disclosed in Scheme V below.##STR19## In Scheme V a mixed protected amine of phenylalaninal, whereBOC is t-butoxycarbonyi and Bn is benzyl, was reacted with potassiumcyanide to form the desired stereoisomeric cyanohydrin (12) in highyield. In additional to the stereospecificity of the cyanohydrinreaction, this process has the added advantage of being easier and lessexpensive because the temperature of the reactions need no: be less than-5° C.

The aminourea (9) was also prepared utilizing the procedure as disclosedin Scheme VI below. ##STR20## The procedure in Scheme VI required onlyone protecting group, BOC, for the amine of the hydroxyamino acid. Thisprocedure has the advantage of having the desired stereochemistry of thebenzyl and hydroxy groups established in the starting material. Thus thechirality does not need to be introduced with the resulting loss ofmaterial due to preparation of diastereomers.

EXAMPLE 1 β-2- Bis (phenylmethyl) amino! benzenepropanol

Method 1

Step 1: Benzylation of L-Phenylalanine

A solution of L-phenylalanine (50.0 g, 0.302 mol), sodium hydroxide(24.2 g, 0.605 mol) and potassium carbonate (83.6 g, 0.605 mol) in water(500 mL) was heated to 97° C. Benzyl bromide (108.5 mL, 0.605 mol) wasthen slowly added (addition time--25 min). The mixture was stirred at97° C. for 30 minutes under a nitrogen atmosphere. The solution wascooled to room temperature and extracted with toluene (2×250 mL). Thecombined organic layers were washed with water and brine, dried overmagnesium sulfate, filtered and concentrated to an oil. The identity ofthe product was confirmed as follows. Analytical TLC (10% ethylacetate/hexane, silica gel) showed major component at Rf value=0.32 tobe the desired tribenzylated compound,N,N-bis(phenylmethyl)-L-phenylalanine phenylmethyl ester. This compoundcan be purified by column chromatography (silica gel, 15% ethylacetate/hexanes). Usually the product is pure enough to be used directlyin the next step without further purification. ¹ H NMR spectrum was inagreement with published literature. ¹ H NMR (CDCL₃) ∂, 3.00 and 3.14(ABX-system, 2H, J_(AB) =14.1 Hz, J_(AX) =7.3 Hz and J_(BX) =5.9 Hz),3.54 and 3.92 (AB-System, 4 H, J_(AB) =13.9 Hz), 3.71 (t, 1H, J=7.6 Hz),5.11 and 5.23 (AB-System, 2H, J_(AB) =12.3 Hz), and 7.18 (m, 20 H).EIMS: m/z 434 (M-1).

Step 2: βS-2- Bis(phenylmethyl)amino!benzenepropanol from the DIBALReducticn of N,N-bislphenylmethyl)-L-Phenylalanine phenylmechyl ester

The benzylated phenylalanine phenylmethyl ester (0.302 mol) from theprevious reaction was dissolved in toluene (750 mL) and cooled to -55°C. A 1.5M solution of DIBAL in toluene (443.9 mL, 0.666 mol) was addedat a rate to maintain the temperature between -55 to -50° C. (additiontime--1 hr). The mixture was stirred for 20 minutes under a nitrogenatmosphere and then quenched at -55° C. by the slow addition of methanol(37 ml). The cold solution was then poured into cold (5° C.) 1.5N HClsolution (1.8 L). The precipitated solid (approx. 138 g) was filteredoff and washed with toluene. The solid material was suspended in amixture of toluene (400 mL) and water (100 ml). The mixture was cooledto 5° C. and treated with 2.5N NaOH (186 mL) and then stirred at roomtemperature until solid dissolved. The toluene layer was separated fromthe aqueous phase and washed with water and brine, dried over magnesiumsulfate, filtered and concentrated to a volume of 75 mL (89 g) Ethylacetate (25 mL) and hexane (25 mL) were added to the residue upon whichthe desired alcohol product began to crystallize. After 30 min, anadditional 50 mL hexane were added to promote further crystallization.The solid was filtered off and washed with 50 mL hexane to give 34.9 gof first crop product. A second crop of product (5.6 g) was isolated byrefiltering the mother liquor. The two crops were combined andrecrystallized from ethyl acetate (20 mL) and hexane (30 mL) to give 40g of βS-2- Bis(phenyl-methyL)amino!benzenepropanol, 40% yield fromL-phenylalanine. An additional 7 g (7%) of product can be obtained fromrecrystallyzation of the concentrated mother liquor. TLC of productRf=0.23 (10% ethyl acetate/hexane, silica gel); ¹ H NMR (CDCl₃) ∂ 2.44(m, 1H,), 3.09 (m, 2H), 3.33 (m, 1H), 3.48 and 3.92 (AB-System, 4H,J_(AB) =13.3 Hz), 3.52 (m, 1H) and 7.23 (m, 15H); α!D²⁵ +42.4 (c 1.45,CH₂ Cl₂); DSC 77.67° C.; Anal. Calcd. for C₂₃ H₂₅ ON: C, 83.34; H, 7.60;N, 4.23. Found: C, 83.43; H, 7.59; N, 4.22. HPLC on chiral stationaryphase: Cyclobond I SP column (250×4.6 mm I.D.), mobile phase:methanol/triethyl ammonium acetate buffer pH 4.2 (58:42, v/v), flow-rateof 0.5 ml/min, detection with detector at 230 nm and a temperature of 0°C. Retention time: 11.25 min., retention time of the desired productenantiomer: 12.5 min.

Method 2

Preparation of βS-2- Bis(phenylmethyl)amino!benzene-propanol from theN,N-Dibenzylation of L-Phenylalaninol:

L-phenylalaninol (176.6 g, 1.168 mol) was added to a stirred solution ofpotassium carbonate (484.6 g, 3.506 mol) in 710 mL of water. The mixturewas heated to 65° C. under a nitrogen atmosphere. A solution of benzylbromide (400 g, 2.339 mol) in 3A ethanol (305 mL) was added at a ratethat maintained the temperature between 60°-68° C. The biphasic solutionwas stirred at 65° C. for 55 min and then allowed to cool to 10° C. withvigorous stirring. The oily product solidified into small granules. Theproduct was diluted with 2.0 L of tap water and stirred for 5 minutes todissolve the inorganic by products. The product was isolated byfiltration under reduced pressure and washed with water until the pH is7. The crude product obtained was air dried overnite to give a semi-drysolid (407 g) which was recrystallized from 1.1 L of ethylacetate/heptane (1:10 by volume). The product was isolated by filtration(at -8° C. washed with 1.6 L of cold (-10° C. ) ethyl acetate/heptane(1:10 by volume) and air-dried to give 339 g 88% yield) of βS-2- Bis(phenylmethyl)amino!benzene-propanol, mp 71.5°-73.0° C. More product canbe obtained from the mother liquor if necessary. The other analyticalcharacterization was identical co compound prepared as described inMethod 1.

EXAMPLE 2 αS- Bis(phenylmethyl)amino!benzenepropanaldehyde

Method 1

βS-2- Bis(phenylmethyl)amino!benzene-propanol (200 g, 0.604 mol) wasdissolved in triethylamine (300 mL, 2.15 mol). The mixture was cooled to12° C. and a solution of sulfur trioxide/pyridine complex (380 g, 2.39mol) in DMSO (1.6 L) was added at a rate to maintain the temperaturebetween 8°-17° C. (addition time--1.0 h). The solution was stirred atambient temperature under a nitrogen atmosphere for 1.5 hour at whichtime the reaction was complete by TLC analysis (33% ethylacetate/hexane, silica gel). The reaction mixture was cooled with icewater and quenced with 1.6 L of cold water (10°-15° C.) over 45 minutes.The resultant solution was extracted with ethyl acetate (2.0 L), washedwith 5% citric acid (2.0 L), and brine (2.2 L), dried over MgSO₄ (280 g)and filtered. The solvent was removed on a rotary evaporator at 35°-40°C. and then dried under vaccuum to give 198.8 g of αS-Bis-(phenylmethyl)amino!-benzenepropanaldehyde as a pale yellow oil(99.9%). The crude product obtained was pure enough co be used directlyin the next step without purification. The analytical data of thecompound were consistent with the published literature. α!D²⁵ =-92.9° (c1.87, CH₂ Cl₂); ¹ H NMR (400 MHz, CDCl₃) ∂, 2.94 and 3.15 (ABX-System,2H, J_(AB) =13.9 Hz, J_(AX) =7.3 Hz and J_(BX) =6.2 Hz), 3.56 (t, 1H,7.1 Hz), 3.69 and 3.82 (AB-System, 4H, J_(AB) =13.7 Hz), 7.25 (m, 15H)and 9.72 (s, 1H); HRMS calcd for (M+1) C₂₃ H₂₄ NO 330.450, found:330.1836. Anal. Calcd. for C₂₃ H₂₃ ON: C, 83.86; H, 7.04; N, 4.25.Found: C, 83.64; H, 7.42; N, 4.19. HPLC on chiral stationary phase:(S,S) Pirkle-Whelk-O 1 column (250×4.6 mm I.D.), mobile phase:hexane/isopropanol (99.5:0.5, v/v), flow-rate: 1.5 ml/min, detectionwith UV detector at 210 nm. Retention time of the desired S-isomer: 8.75min., retention time of the R-enanatiomer 10.62 min.

Method 2

A solution of oxalyl chloride (8.4 ml, 0.096 mol) in dichloromethane(240 ml) was cooled to -74° C. A solution of DMSO (12.0 ml, 0.155 mol)in dichloromethane (50 ml) was then slowly added at a rate to maintainthe temperature at -74° C. (addition time ˜1.25 hr). The mixture wasstirred for 5 min. followed by addition of a solution of βS-2-bis(phenylmethyl)amino!benzene-propanol (0.074 mol) in 100 ml ofdichloromethane (addition time --20 min., temp. -75° C. to -68° C.). Thesolution was stirred at -78° C. for 35 minutes under a nitrogenatmosphere. Triethylamine (41.2 ml, 0.295 mol) was then added over 10min. (temp. -78° to -68° C.) upon which the ammonium salt precipitated.The cold mixture was stirred for 30 min. and then water (225 ml) wasadded. The dichloromethane layer was separated from the aqueous phaseand washed with water, brine, dried over magnesium sulfate, filtered andconcentrated. The residue was diluted with ethyl acetate and hexane andthen filtered to further remove the ammonium salt. The filtrate wasconcentrated to give αS- bis(phenylmethyl)amino!benzenepropanaldehyde.The aldehyde was carried on to the next step without purification.

Method 3

To a mixture of 1.0 g(3.0 mmoles) of βS-2-bis(phenylmethyl)amino!benzenepropanol 0.531 g(4.53 mmoles) of N-methylmorpholine, 2.27 g of molecular sieves(4A) and 9.1 mL of acetonitrilewas added 53 mg(0.15 mmoles) of tetrapropylammonium perruthenate(TPAP).The mixture was stirred for 40 minutes at room temperature andconcentrated under reduced pressure. The residue was suspended in 15 mLof ethyl acetate, filtered through a pad of silica gel. The filtrate wasconcentrated under reduced pressure to give a product containingapproximately 50% of αS-2- bis(phenylmethyl)amino!benzene propanaldehydeas a pale yellow oil.

Method 4

To a solution of 1.0 g (3.02 mmoles) of βS-2-bis(phenylmethyl)amino!benzenepropanol in 9.0 mL of toluene was added4.69 mg(0.03 mmoles) of 2,2,6,6-tetramethyl-1-piperidinyloxy, freeradical (TEMPO), 0.32 g(3.11 mmoles) of sodium bromide, 9.0 mL of ethylacetate and 1.5 mL of water. The mixture was cooled to 0° C. and anaqueous solution of 2.87 mL of 5% household bleach containing 0.735g(8.75 mmoles) of sodium bicarbonate and 8.53 mL of water was addedslowly over 25 minutes. The mixture was stirred at 0° C. for 60 minutes.Two more additions (1.44 mL each) of bleach was added followed bystirring for 10 minutes. The two phase mixture was allowed to separate.The aqueous layer was extracted twice with 20 mL of ethyl acetate. Thecombined organic layer was washed with 4.0 mL of a solution containing25 mg of potassium iodide and water(4.0 mL), 20 mL of 10% agueous sodiumthiosulfate solution and then brine solution. The organic solution wasdried over magnesium sulfate, filtered and concentrated under reducedpressure to give 1.34 g of crude oil containing a small amount of thedesired product aldehyde, αs-bis(phenylmethyl)amino!benzenepropanaldehyde.

Method 5

Following the same procedures as described in Example 2 (Method 1)except 3.0 equivalents of sulfur trioxide pyridine complex was used andαS- bis(phenylmethyl)amino!benzenepropanaldehyde was isolated incomparable yields.

EXAMPLE 3 N,N,αS-Tris(phenylmethyl)-2S-oxiranemethanamine

Method 1

A solution of αS- Bis(phenylmethyl)amino!benzene-propanaldehyde (191.7g, 0.58 mol) and chloroiodomethane (56.4 mL, 0.77 mol) intetrahydrofuran (1.8 L) was cooled to -30° to -35° C. (coldertemperature such as -70° C. also worked well but warmer temperatures aremore readily achieved in large scale operations) in a stainless steelreactor under a nitrogen atmosphere. A solution of n-butyllithium inhexane (1.6M, 365 mL, 0.58 mol) was then added at a rate that maintainedthe temperature below -25° C. After addition the mixture was stirred at-30° to -35° C. for 10 minutes. More additions of reagents were carriedout in the following manner: (1) additional chloroiodomethane (17 mL)was added, followed by n-butyllithium (110 mL) at <-25° C. Afteraddition the mixture was stirred at -30° to -35° C. for 10 minutes. Thiswas repeated once. (2) Additional chloroiodomethane (8.5 mL, 0.11 mol)was added, followed by n-butyllithium (55 mL, 0.088 mol) at <-25° C.After addition the mixture was stirred at -30° to -35° C. for 10minutes. This was repeated 5 times. (3) Additional chloroiodomethane(8.5 mL, 0.11 mol) was added, followed by n-butyllithium (37 mL, 0.059mol) at <-25° C. After addition the mixture was stirred at -30° to -35°C. for 10 minutes. This was repeated once. The external cooling wasstopped and the mixture warmed to ambient temp. over 4 to 16 hours whenTLC (silica gel, 20% ethyl acetate/hexane) indicated that the reactionwas completed. The reaction mixture was cooled to 10° C. and quenchedwith 1452 g of 16% ammonium chloride solution (prepared by dissolving232 g of ammonium chloride in 1220 mL of water), keeping the temperaturebelow 23° C. The mixture was stirred for 10 minutes and the organic andaqueous layers were separated. The aqueous phase was extracted withethyl acetate (2×500 mL). The ethyl acetate layer was combined with thetetrahydrofuran layer. The combined solution was dried over magnesiumsulfate (220 g), filtered and concentrated on a rotary evaporator at 65°C. The brown oil residue was dried at 70° C. in vacuo (0.8 bar) for 1 hto give 222.8 g of crude material. (The crude product weight was >100%.Due to the relative instability of the product on silica gel, the crudeproduct is usually used directly in the next step without purification).The diastereomeric ratio of the crude mixture was determined by protonNMR: (2S)/(2R): 86:14. The minor and major epoxide diastereomers werecharacterized in this mixture by tlc analysis (silica gel, 10% ethylacetate/hexane), Rf=0.29 & 0.32, respectively. An analytical sample ofeach of the diastereomers was obtained by purification on silica-gelchromatography (3% ethyl acetate/hexane) and characterized as follows:

N,N,αS-Tris(phenylmethyl)-2S-oxiranemethanamine

¹ H NMR (400 MHz, CDCl₃) ∂ 2.49 and 2.51 (AB-System, 1H, J_(AB) =2.82),2.76 and 2.77 (AB-System, 1H, J_(AB) =4.03), 2.83 (m, 2H), 2.99 & 3.03(AB-System, 1H, J_(AB) =10.1 Hz), 3.15 (m, 1H), 3.73 & 3.84 (AB-System,4H, J_(AB) =14.00), 7.21 (m, 15H); ¹³ C NMR (400 MHz,CDCl₃) ∂ 139.55,129.45, 128.42, 128.14, 128.09, 126.84, 125.97, 60.32, 54.23, 52.13,45.99, 33.76; HRMS calcd for C₂₄ H₂₆ NO (M+1) 344.477, found 344.2003.

N, N,αS-Tris (phenylmethyl) -2R-oxiranemethanamine

¹ H NMR (300 MHz, CDCl₃) ∂ 2.20 (m, 1H), 2.59 (m, 1H), 2.75 (m, 2H),2.97 (m, 1H), 3.14 (m, 1H), 3.85 (AB-System, 4H), 7.25 (m, 15H).HPLC onchiral stationary phase: Pirkle-Whelk-O 1 column (250×4.6 mm I.D.),mobile phase: hexane/isopropanol (99.5:0.5, v/v), flow-rate: 1.5 ml/min,detection with UV detector at 210 nm. Retention time of(8): 9.38 min.,retention time of enanatiomer of (4): 13.75 min.

Method 2

A solution of the crude aldehyde 0.074 mol and chloroiodomethane (7.0ml, 0.096 mol) in tetrahydrofuran (285 ml) was cooled to -78° C., undera nitrogen atmosphere. A 1.6M solution of n-butyllithium in hexane (25ml, 0.040 mol) was then added at a rate to maintain the temperature at-75° C. (addition time--15 min.). After the first addition, additionalchloroiodomethane (1.6 ml, 0.022 mol) was added again, followed byn-butyllithium (23 ml, 0.037 mol), keeping the temperature at -75° C.The mixture was stirred for 15 min. Each of the reagents,chioroiodomethane (0.70 ml, 0.010 mol) and n-butyllithium (5 ml, 3.008mol) were added 4 more times over 45 min. at -75° C. The cooling bathwas then removed and the solution warmed to 22° C. over 1.5 hr. Themixture was poured into 300 ml of saturated aq. ammonium chloridesolution. The tetrahydrofuran layer was separated. The aqueous phase wasextracted with ethyl acetate (1×300 ml). The combined organic layerswere washed with brine, dried over magnesium sulfate, filtered andconcentrated to give a brown oil (27.4 g). The product could be used inthe next step without purification. The desired diastereomer can bepurified by recrystallization at a subsequent step. The product couldalso be purified by chromatography.

Method 3

A solution of αS- Bis(phenylmethyl)amino!benzene-propanaldehyde (178.84g, 0.54 mol) and bromochloromethane (46 mL, 0.71 mol) in tetrahydrofuran(1.8 L) was cooled to -30° to -35° C. (colder temperature such as -70°C. also worked well but warmer temperatures are more readily achieved inlarge scale operations) in a stainless steel reactor under a nitrogenatmosphere. A solution of n-butyllithium in hexane (1.6M, 340 mL, 0.54mol) was then added at a rate that maintained the temperature below -25°C. After addition the mixture was stirred at -30° to -35° C. for 10minutes. More additions of reagents were carried out in the followingmanner: (1) additional bromochloromethane (14 mL) was added, followed byn-butyllithium (102 mL) at <-25° C. After addition the mixture wasstirred at -30° to -35° C. for 10 minutes. This was repeated once. (2)Additional bromochloromethane (7 mL, 0.11 mol) was added, followed byn-butyllithium (51 mL, 0.082 mol) at <-25° C. After addition the mixturewas stirred at -30° to -35° C. for 10 minutes. This was repeated 5times. (3) Additional bromochioromethane (7 mL, 0.11 mol) was added,followed by n-butyllithium (51 mL, 0.082 mol) at <-25° C. After additionthe mixture was stirred at -30° to -35° C. for 10 minutes. This wasrepeated once. The external cooling was stopped and the mixture warmedto ambient temp. over 4 to 16 hours when TLC (silica gel, 20% ethylacetate/hexane) indicated that the reaction was completed. The reactionmixture was cooled to 10° C. and quenched with 1452 g of 16% ammoniumchloride solution (prepared by dissolving 232 g of ammonium chloride in1220 mL of water), keeping the temperature below 23° C. The mixture wasstirred for 10 minutes and the organic and aqueous layers wereseparated. The aqueous phase was extracted with ethyl acetate (2×500mL). The ethyl acetate layer was combined with the tetrahydrofuranlayer. The combined solution was dried over magnesium sulfate (220 g),filtered and concentrated on a rotary evaporator at 65° C. The brown oilresidue was dried at 70° C. in vacuo (0.8 bar) for 1 h to give 222.8 gof crude material.

Method 4

Following the same procedures as described in Example 3 (Method 3)except the reaction temperatures were at -20° C. The resultingN,N,αS-tris(phenylmethyl)-2S-oxiranemethanamine was a diastereomericmixture of lesser purity then that of Method 3.

Method 5

Following the same procedures as described in Example 3 (Method 3)except the reaction temperatures were at -70°-78° C. The resultingN,N,αS-tris(phenylmethyl)-2S-oxiranemethanamine was a diastereomericmixture, which was used directly in the subsequent steps withoutpurification.

Method 6

Following the same procedures as described in Example 3 (Method 3)except a continuous addition of bromochloromethane and n-butyllithiumwas used at -30° to -35° C. After the reaction and work up procedures asdecribed in Example 3 (Method 3), the desiredN,N,αS-tris(phenylmethyl)-2S-oxiranemethanamine was isolated incomparable yields and purities.

Method 7

Following the same procedures as described in Example 3 (Method 2)except dibromomethane was used instead of chloroiodomethane. After thereaction and work up procedures as decribed in Example 3 (Method 2), thedesired N,N,αS-tris(phenylmethyl)-2S-oxiranemethanamine was isolated.

EXAMPLE 4 3S-N,N-Bis(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-ol

To a solution of crude N,N,αS-tris(phenylmethyl)-2S-oxiranemethanamine(388.5 g, 1.13 mol) from Example 3 in isopropanol (2.7 L) (or ethylacetate) was added isobutylamine (1.7 kgm, 23.1 mol) over 2 min. Thetemperature increased from 25° C. to 30° C. The solution was heated to82° C. and stirred a this temperature for 1.5 h. The warm solution wasconcentrated under reduced pressure at 65° C. The brown oil residue wastransferred to a 3-L flask and dried in vacuo (0.8 mm Hg) for 16 h togive 450 g of 3S-N,N-bis(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olas a crude oil. The product was used directly in the next step withoutpurification. An analytical sample of the desired major diastereomericproduct was obtained by purifying a small sample of crude product bysilica gel chromatography (40% ethyl acetate/hexane). Tlc analysis:silica gel, 40% ethyl acetate/hexane; Rf=0.28; HPLC analysis:ultrasphere ODS column, 25% triethylamine-/phosphate buffer pH3/acetonitrile, flow rate 1 mL/min, UV detector; retention time 7.49min.; HRMS calcd for C28H37N2O (M+1) 417.616, found 417.2887.

An analytical sample of the minor diastereomeric product, 3S-N,N-bis(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2S-olwas also obtained by purifying a small sample of crude product by silicagel chromatography (40% ethyl acetate/hexane).

EXAMPLE 5 3S-N,N-Bis(phenylmethyl)amino!-1-(3-methylbutyl)amino-4-phenylbutan-2R-ol

Example 4 was followed using isoamylamine instead of isobutylamine toprepare 3S-N,N-Bis(phenylmethyl)amino!-1-(3-methylbutyl)amino-4-phenylbutan-2R-oland 3S-N,N-Bis(phenylmethyl)amino!-(3-methylbutyl)amino-4-phenylbutan-2S-ol incomparable yields to that of Example 4. The crude amine was used in thenext step without further purification.

EXAMPLE 6 N- 3S-N,N-Bis(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

A solution of the crude 3S-N,N-Bis(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-ol(446.0 g, 1.1 mol) from Example 4 in tetrahydrofuran (6 L) (or ethylacetate) was cooled to 8° C. t-Butyl isocyanate (109.5 g, 1.1 mol) wasthen added to the solution of the amine from an addition funnel at arate that maintained the temperature between 10°-12° C. (addition timewas about 10 min). The external cooling was stopped and the reaction waswarmed to 18° C. after 30 min. The solution was transferred directlyfrom the reactor to a rotary evaporator flask (10 L) through a teflontube using vacuum and then concentrated. The flask was heated in a 50°C. water bath during the 2 h required for the distillation of thesolvent. The brown residue was dissolved in ethyl acetate (3 L), washedwith 5% aq citric acid solution (1×1.2 L), water (2×500 mL), brine(1×400 mL), dried over magnesium sulfate (200 g) and filtered. Thevolume of product solution was reduced to 671 mL over 2 h on a rotaryevaporator at 50° C. The concentrate was stirred and diluted with 1.6 Lof hexane. The mixture was cooled to 12° C. and stirred for 15 hours.The product crystals were isolated by filtration, washed with 10% ethylacetate/hexane (1×500 mL), hexane (1×200 mL) and dried in vacuo (2 mm)at 50° C. for 1 hour to give 248 g of N- 3S- N,N-bis-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)-urea.The mother liquor and washes were combined and concentrated on a rotaryevaporator to give 270 g of a brown oil. This material was dissolved inethyl acetate (140 mL) at 50° C. and diluted with hexane (280 mL) andseeded with crystals of the first crop product (20 mg). The mixture wascooled in an ice bath and stirred for 1 h. The solid was isolated byfiltration, washed with 10% ethyl acetate/hexane (1×200 mL) and dried invacuo (2 mm) at 50° C. for 1 h to give 55.7 g of 11 as the second crop(49% overall yield). Mp 126° C.; α!D25=-59.0° (c=1.0, CH2C12), TLC: Rf0.31 (silica gel, 25% ethyl acetate/hexane).

An analytical sample of the minor diasatereomer, N- 3S-N,N-bis(phenylmethyl)amino!-2S-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureawas isolated by silica-gel chromatography (10-15% ethyl acetate/hexane)in an earlier experiment and characterized.

EXAMPLE 7 N- 3S-N,N-Bis(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)urea

The crude product from Example 5 was reacted with t-butylisocyanatefollowing the method of Example 6 to prepare N- 3S-N,N-Bis(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)ureaand N- 3S-N,N-Bis(phenylmethyl)amino!-2S-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)ureain comparable yields to that of Example 6.

EXAMPLE 8 N-3S-Amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

N- 3S-N,N-Bis(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea(125.77 g, 0.244 mol) from Example 6 was dissolved in ethanol (1.5 L)(or methanol) and 20% palladium hydroxide on carbon (18.87 g) (or 4%palladium on carbon) was added to the solution under nitrogen. Themixture was stirred at ambient temperature under a hydrogen atmosphereat 60 psi for approximately 8 h. The catalyst was removed by filtrationand the filtrate was concentrated to give 85 g of N-3S-Amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a colorless oil.

EXAMPLE 9 N-3S-Amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)urea

N- 3S-N,N-Bis(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)ureafrom Example 7 was hydrogenated following the method of Example 8 toprepare N-3S-Amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)ureain comparable yields to Example 8.

EXAMPLE 10 N-benzyl-L-phenylalaninol

Method 1

L-Phenylalaninol (89.51 g, 0.592 moles) was dissolved in 375 mL ofmethanol under inert atmosphere, 35.52 g (0.592 moles) of glacial aceticacid and 50 mL of methanol was added followed by a solution of 62.83 g(0.592 moles) of benzaldehyde in 100 mL of methanol. The mixture wascooled to approximately 15° C. and a solution of 134.6 g(2.14 moles) ofsodium cyanoborohydride in 700 mL of methanol was added in approximately40 minutes, keeping the temperature between 15° C. and 25° C. Themixture was stirred at room temperature for 18 hours. The mixture wasconcentrated under reduced presssure and partitioned between 1 L of 2Mammonium hydroxide solution and 2 L of ether. The ether layer was washedwith 1 L of 1M ammonium hydroxide solution, twice with 500 mL water, 500mL of brine and dried over magnesium sulfate for 1 hour. The ether layerwas filtered, concentrated under reduced pressure and the crude solidproduct was recrystallized from 110 mL of ethyl acetate and 1.3 L ofhexane to give 115 g (81% yield) of N-benzyl-L-phenylalaninol as a whitesolid.

Method 2

L-Phenylalaninol (5 g, 33 mmoles) and 3.59 g (33.83 mmoles) ofbenzaldehyde were dissolved in 55 mL of 3A ethanol under inertatmosphere in a Parr shaker and the mixture was warmed to 60° C. for 2.7hours. The mixture was cooled to approximately 25° C. and 0.99 g of 5%platinum on carbon was added and the mixture was hydrogenated at 60 psiof hydrogen and 40° C. for 10 hours. The catalyst was filtered off, theproduct was concentrated under reduced pressure and the crude solidproduct was recrystallized from 150 mL of heptane to give 3.83 g(48%yield) of N-benzyl-L-phenylalaninol as a white solid.

EXAMPLE 11 N-(t-Butoxycarbonyl)-N-benzyl-L-phenylalaninol

N-benzyl-L-phenylalaninol (2.9 g, 12 mmoles) from Example 10 wasdissolved in 3 mL of triethylamine and 27 mL of methanol and 5.25 g(24.1mmoles) of di-tert-butyl dicarbonate was added. The mixture was warmedto 60° C. for 35 minutes and concentrated under reduced pressure. Theresidue was dissolved in 150 mL of ethyl acetate and washed twice with10 mL of cold(0°-5° C.), dilute hydrochoric acid (pH 2.5 to 3), 15 mL ofwater, 10 mL of brine, dried over magnesium sulfate, filtered andconcentrated under reduced pressure. The crude product oil was purifiedby silica gel chromatography (ethyl acetate: hexane, 12:3 as elutingsolvent) to give 3.98 g (97% yield) of colorless oil.

EXAMPLE 12 N-(t-Butoxycarbonyl)-N-benzyl-L-phenylalaninal

Method 1

To a solution of 0.32 g(0.94 mmoles) ofN-(t-Butoxycarbonyl)-N-benzyl-L-phenylalaninol from Example 11 in 2.8 mLof toluene was added 2.4 mg (0.015 mmoles) of2,2,6,6-tetramethyl-1-piperidinyloxy, free radical (TEMPO), 0.1 g (0.97mmoles) of sodium bromide, 2.8 mL of ethyl acetate and 0.34 mL of water.The mixture was cooled to 0° C. and an aqueous solution of 4.2 mL of 5%household bleach containing 0.23 g 3.0 mL, 2.738 mmoles) of sodiumbicarbonate was added slowly over 30 minutes. The mixture was stirred at0° C. for 10 minutes. Three more additions (0.4 mL each) of bleach wasadded followed by stirring for 10 minutes after each addition to consumeall the stating material. The two phase mixture was allowed to separate.The aqueous layer was extracted twice with 8 mL of zoluene. The combinedorganic layer was washed with 1.25 mL of a solution containing 0.075 gof potassium iodide, sodium bisulfate(0.125 g) and water(1.1 mL), 1.25mL of 10% aqueous sodium thiosulfate solution, 1.25 mL of pH 7 phosphatebuffer and 1.5 mL of brine solution. The organic solution was dried overmagnesium sulfate, filtered and concentrated under reduced pressure togive 0.32 g (100% yield) ofN-(t-Butoxycarbonyl)-N-benzyl-L-phenylalaninal.

Method 2

To a solution of 2.38 g(6.98 mmoles) ofN-(t-butoxycarbonyl)-N-benzyl-L-phenylalaninol from Example 11 in 3.8 mL(27.2 mmoles) of triethylamine at 10° C. was added a solution of 4.33 g(27.2 mmoles) of sulfur trioxide pyridine complex in 17 mL of dimethylsulfoxide. The mixture was warmed to room temperature and stirred forone hour. Water (16 mL) was added and the mixture was extracted with 20mL of ethyl acetate. The oragnic layer was washed with 20 mL of 5%citric acid, 20 mL of water, 20 mL of brine, dried over magnesiumsulfate and filtered. The filtrate was concentrated under reducedpressure to give 2.37 g(100% yield) ofN-(t-Butoxycarbonyl)-N-benzyl-L-phenylalaninal.

EXAMPLE 13 N,αS-Bis(phenylmethyl) -N- (t-butoxycarbonyl)-2S-oxiranemethanamine

Method 1

A solution of 2.5 g (7.37 mmoles) ofN-(t-butoxycarbonyl)-N-benzyl-L-phenylalaninal from Example 12 and 0.72mL of chloroiodomethane in 35 mL of THF was cooled to -78° C. A 4.64 mLof a solution of n-butyllithium (1.6M in hexane, 7.42 mmoles) was addedslowly, keeping the temperature below -70° C. The mixture was stirredfor 10 minutes between -70° to -75° C. Two additional portions of 0.22mL of chloroiodomethane and 1.4 mL of n-butyllithium was addedsequentially and the mixture was stirred for 10 minutes between -70° to-75° C. after each addition. Four additional portions of 0.11 mL ofchloroiodomethane and 0.7 mL of n-butyllithium was added sequentiallyand the mixture was stirred for 10 minutes between -70° to -75° C. aftereach addition. The mixture was warmed to room temperature for 3.5 hours.The product was quenched at below 5° C. with 24 mL of ice-cold water.The biphasic layers were separated and the aqueous layer was extractedtwice with 30 mL of ethyl acetate. The combined organic layers waswashed three times with 10 mL water, then with 10 mL brine, dried oversodium sulfate, filtered and concentrated under reduced pressure to give2.8 g of a yellow crude oil. This crude oil (>100% yield) is a mixtureof the diastereomeric epoxidesN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2S-oxiranemethanamine andN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2R-oxiranemethanamine. Thecrude mixture is used directly in the next step without purification.

Method 2

To a suspension of 2.92 g (13.28 mmoles) of trimethylsulfoxonium iodidein 45 mL of acetonitrile was added 1.49 g (13.28 mmoles) of potassiumt-butoxide. A solution of 3.0 g (8.85 mmoles) ofN-(t-butoxycarbonyl)-N-benzyl-L-phenylalaninal from Example 12 in 18 mLof acetonitrile was added and the mixture was stirred at roomtemperature for one hour. The mixture was diluted with 150 mL of waterand extracted twice with 200 mL of ethyl acetate. The organic layerswere combined and washed with 100 mL water, 50 mL brine, dried oversodium sulfate, filtered and concentrated under reduced pressure to give3.0 g of a yellow crude oil. The crude product was purified by silicagel chromatography (ethyl acetate/hexane: 1:8 as eluting sovent) to give1.02 g (32.7% yield) of a mixture of the two diastereomersN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2S-oxiranemethanamine andN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2R-oxiranemethanamine.

Method 3

To a suspension of 0.90 g (4.42 mmoles) of trimethylsulfonium iodide in18 mL of acetonitrile was added 0.495 g (4.42 mmoles) of potassiumt-butoxide. A solution of 1.0 g (2.95 mmoles) ofN-(t-butoxycarbonyl)-N-benzyl-L-phenylalaninal from Example 12 in 7 mLof acetonitrile was added and the mixture was stirred at roomtemperature for one hour. The mixture was diluted with 80 mL of waterand extracted twice with 80 mL of ethyl acetate. The organic layers werecombined and washed with 100 mL water, 30 mL brine, dried over sodiumsulfate, filtered and concentrated under reduced pressure to give 1.04 gof a yellow crude oil. The crude product was a mixture of the twodiascereomersN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2S-oxiranemethanamine andN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2R-oxiranemethanamine.

EXAMPLE 14 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-ol

To a solution of 500 mg (1.42 mmoles) of the crude epoxide from Example13 in 0.98 mL of isopropanol was added 0.71 mL (7.14 mmoles) ofisobutylamine. The mixture was warmed to reflux at 85° C. to 90° C. for1.5 hours. The mixture was concentrated under reduced pressure and theproduct oil was purified by silica gel chromatography(chloroform:methanol, 100:6 as eluting solvents) to give 330 mg of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olas a colorless oil (54.5% yield). 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2S-olwas also isolated. When purifiedN,αS-bis(phenylmethyl)-N-(t-butoxycarbonyl)-2S-oxiranemethanamine wasused as starting material, 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olwas isolated after purification by chromatography in an 86% yield.

EXAMPLE 15 N- 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 309 mg (0.7265 mmoles) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olfrom Example 14 in 5 mL of THF was added 0.174 mL(1.5 mmoles) oft-butylisocyanate. The mixture was stirred at room temperature for 1.5hours. The product was concentrated under reduced pressure to give 350mg (92% yield) of a white solid crude product. The crude product waspurified by silica gel chromatography (ethyl acetate/hexane: 1:4 aseluting solvents) to give 324 mg of N- 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a white solid (85.3% yield).

EXAMPLE 16 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-2S-hydroxy-4-phenylbutyronitrile

A solution of 7.0 g (20.65 mmoles) ofN-(t-butoxycarbonyl)-N-benzyl-L-phenylalaninal from Example 12 in 125 mLof THF was cooled to -5° C. A solution of 12.96 g of sodium bisulfite in68 mL of water was added over 40 minutes, keeping the temperature below5° C. The mixture was stirred for 3 hours at 0° to 5° C. An additional1.4 g of sodium bisulfite was added and the mixture was stirred foranother two hours. Sodium cyanide (3.3 g, 82.56 mmoles) was added to thebisulfite product at 0° to 5° C. and the mixture was stirred at roomtemperature for 16 hours. The biphasic mixture was extracted with 150 mLof ethyl acetate. The aqueous layer was extracted twice each with 100 mLof ethyl acetate. The combined organic layers was washed twice with 30mL water, twice with 25 mL brine, dried over sodium sulfate, filteredand concentrated under reduced pressure to give 7.5 g (100% crude yieldof both diastereomers) of crude oil. The crude oil was purified bysilica gel chromatography (ethyl acetate:hexane, 1:4 as elutingsolvents) to give 5.725 g (76% yield) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-2S-hydroxy-4-phenylburyronitrileas the major later eluting diastereomer and 0.73 g (9.6% yield) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyronitrileas the minor diastereomer. The combined yields of both isomers ofcyanohydrins is 85.6% yield.

EXAMPLE 17 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-1-amino-4-phenylbutan-2R-ol

To a solution of 205.5 mg (0.56 mmoles) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-2S-hydroxy-4-phenylbutyronitrilefrom Example 16 in 4 mL of THF was added 2.4 mL of a solution of boranein THF (1.0M, 4 mmoles). The mixture was stirred at room temperature for30 minutes. An additional 1.4 mL of borane in THF was added and themixture was stirred for another 30 minutes. The mixture was cooled to 0°C. and 2.0 mL of cold (0°-5° C.) water was added slowly. The mixture waswarmed to room temperature and stirred for 30 minutes. The product wasextracted twice with 30 mL of ethyl acetate. The oragnic layers werecombined and washed with 4 mL water, 4 mL brine, dried over sodiumsulfate, filtered and concentrated under reduced pressure to give 200 mgof 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-amino-4-phenylbutan-2R-olas a white solid (96.4% yield).

EXAMPLE 18 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-ol

To a solution of 2.41 g (6.522 mmoles) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-amino-4-phenylbutan-2R-olfrom Example 17 in 40 mL of methanol was added 0.592 mL (6.522 mmoles)of isobutyraldehyde and 0.373 mL (6.522 mmoles) of acetic acid. Themixture was stirred for 10 minutes. Sodium cyanoborohydride (1.639 g, 26mmoles) was added and the mixture was stirred for 16 hours at roomtemperature. The product mixture was concentrated under reduced pressureand partitioned beween 150 mL of ethyl acetate and 50 mL of 1.5Mammonium hydroxide. The organic layer was washed twice with 20 mL water,twice with 20 mL brine, dried over sodium sulfate, filtered andconcentrated to an yellow oil. The crude product was purified by silicagel chromatography (chloroform:methanol, 100:6 as eluting solvents) togive 2.326 g of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olas a colorless oil (88.8% yield).

EXAMPLE 19 N- 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 309 mg(0.7265 mmoles) of 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olfrom Example 18 in 5 mL of THF was added 0.174 mL(l.5 mmoles) oft-butylisocyanate. The mixture was stirred at room temperature for 1.5hours. The product was concentrated under reduced pressure to give 350mg (92% yield) of a white solid crude product. The crude product waspurified by silica gel chromatography (ethyl acetate/hexane: 1:4 aseluting solvents) to give 324 mg of N- 3S-N-(t-butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a white solid (85.3% yield).

EXAMPLE 20 N- 3S-N-(Phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 210 mg (0.4 mmoles) of N- 3S-N-(t-Butoxycarbonyl)-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureafrom Example 19 in 5.0 mL of THF was added 5 mL of 4N hydrochloric acid.The mixture was stirred at room temperature for two hours. The solventswere removed under reduced pressure to give 200 mg (100%) of N- 3S-N-(phenylmethyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a white solid.

EXAMPLE 21 N-3S-Amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 200 mg (0.433 mmoles) of N- 3S-N-(phenylmethyl)amino!-2R-nydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureafrom Example 20 in 7 mL of 3A ethanol was added 0.05 g of 20% palladiumon carbon. The mixture was hydrogenated at 40° C. for 1.8 hours at 5 psifollowed by hydrogenation at 60 psi at room temperature for 22 hours.The catalyst was filtered and the solvent and by-product were removedunder reduced pressure to give 150 mg (93.4% yield) of N-3S-amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a white solid.

EXAMPLE 22 3S-(N-t-Butoxycarbonyl)amino-4-phenyibutan-1,2R-diol

To a solution of 1 g (3.39 mmoles) of2S-(N-t-butoxycarbonyl)amino-1S-hydroxy-3-phenylbutanoic acid(commercially available from Nippon Kayaku, Japan) in 50 mL of THF at 0°C. was added 50 mL of borane-THF complex (liquid,1.0M in THF), keepingthe temperatures below 5° C. The reaction mixture was warmed to roomtemperature and stirred for 16 hours. The mixture was cooled to 0° C.and 20 mL of water was added slowly to destroy the excess BH₃ and toquench the product mixture, keeping the temperature below 12° C. Thequenched mixture was stirred for 20 minutes and concentrated underreduced pressure. The product mixture was extracted three times with 60mL of ethyl acetate. The organic layers were combined and washed with 20mL of water, 25 mL of saturated sodium chloride solution andconcentrated under reduced pressure to give 1.1 g of crude oil. Thecrude product was purified by silica gel chromatography(chloroform/methanol, 10:6 as eluting solvents) to give 900 mg (94.4%yield) of 3S-(N-t-butoxycarbonyl)amino-4-phenylbutan-1,2R-diol as awhite solid.

EXAMPLE 23 3S-(N-t-Butoxycarbonyl)amino-2R-hydroxy-4-phenylbut-1-ylToluenesulfonate

To a solution of 744.8 mg (2.65 mmoles) of3S-(N-t-butoxycarbonyl)amino-4-phenylbutan-1,2R-diol from Example 22 in13 mL of pyridine at 0° C. was added 914 mg of toluenesulfonyl chloridein one portion. The mixture was stirred at 0° C. to 5° C. for 5 hours. Amixture of 6.5 mL of ethyl acetate and 15 mL of 5% aqueous sodiumbicarbonate solution was added to the reaction mixture and stirred for 5minutes. The product mixture was extracted three times with 50 mL ofethyl acetate. The organic layers were combined and washed with 15 mL ofwater, 10 mL of saturated sodium chloride solution and concentratedunder reduced pressure to give about 1.1 g of a yellow chunky solid. Thecrude product was purified by silica gel chromatography (ethylacetate/hexane 1:3 as eluting solvents) to give 850 mg (74% yield) of3S-(N-t-butoxycarbonyl)amino-2R-hydroxy-4-phenylbut-1-yltoluenesulfonate as a white solid.

EXAMPLE 24 3S-N-(t-Butoxycarbonyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-ol

To a solution of 90 mg (0.207 mmoles) of3S-(N-t-butoxycarbonyl)amino-2R-hydroxy-4-phenylbut-1-yltoluenesulfonate from Example 23 in 0.143 mL of isopropanol and 0.5 mLof toluene was added 0.103 mL (1.034 mmoles) of isobutylamine. Themixture was warmed to 80° to 85° C. and stirred for 1.5 hours. Theproduct mixture was concentrated under reduced pressure at 40° to 50° C.and purified by silica gel chromatography (chloroform/methanol, 10:1 aseluting solvents) to give 54.9 mg (76.8% yield) of 3S-N-(t-butoxycarbonyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olas a white solid.

EXAMPLE 25 N- 3S-N-(t-Butoxycarbonyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 0.1732 g (0.516 mmoles) of 3S-N-(t-butoxycarbonyl)amino!-1-(2-methylpropyl)amino-4-phenylbutan-2R-olfrom Example 24 in 5 mL of ethyl acetate at 0° C. was added 1.62 mL(12.77 mmoles) of t-butylisocyanate and the mixture was stirred for onehour. The product was concentrated under reduced pressure and purifiedby silica gel chromatography (chloroform/methanol, 100:1.5 as elutingsolvents) to give 96 mg (42.9% yield) of N- 3S-N-(t-butoxycarbonyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureaas a white solid.

EXAMPLE 26 N-3S-amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)urea

To a solution of 10 mg (0.023 mmoles) of N- 3S-N-(t-butoxycarbonyl)amino!-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureafrom Example 27 in 1 mL of methanol at 0° C. was added 1.05 mL of a 4Mhydrogen chloride in methanol and the mixture was stirred at roomtemperature for 45 minutes. The product was concentrated under reducedpressure. The residue was dissolved 5 mL of methanol and concentratedunder reduced pressure. This operation was repeated three times toremove water form the product, after which 8.09 mg (95.2% yield) of N-3S-amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(2-methylpropyl)ureahydrochloride salt was obtained as a white solid.

EXAMPLE 27 3S-(N,N-Dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether

To a solution of 24.33 g (73.86 mmol) of2S-(N,N-dibenzyl)amino-3-phenylpropanal in 740 mL of anhydrous methylenechloride at -20° C. under a nitrogen atmosphere, was added 11.8 mL (8.8g, 88.6 mmol) of trimethylsilylcyanide, then 19.96 g (88.6 mmol) ofanhydrous zinc bromide. After 4 hours at -15° C., and 18 hours at roomtemperature, the solvent was removed under reduced pressure, ethylacetate was added, washed with water, brine, dried over magnesiumsulfate, filtered and concentrated to afford 31.3 g of a brown oil,which was identified as a 95:5 mixture of3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether, m/e=429(M+H) and3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether, respectively.

EXAMPLE 28 3S-(N,N-Dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile

A solution of 10.4 g (24.3 mmol) of the crude 95:5 mixture of3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether, and3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether from Example 27 in 40 mL of methanol, was addedto 220 mL of 1N hydrochloric acid with vigorous stirring. The resultingsolid was collected, dissolved in ethyl acetate, washed with aqueoussodium bicarbonate, brine, dried over anhydrous magnesium sulfate,filtered and concentrated to afford 8.04 g of crude product. This wasrecrystallized from ethyl acetate and hexane to afford pure3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile, m/e=357 (M+H).

EXAMPLE 29 3S-(N,N-Dibenzyl)amino-2R-hydroxy-4-phenylbutylamine

Method 1

A solution of 20.3 g (47.3 mmol) of the crude 95:5 mixture of3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether, and3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether from Example 28 in 20 mL of anhydrous diethylether, was added to 71 mL (71 mmol) of a 1M solution of lithium aluminumhydride in diethyl ether at reflux. After the addition, the reaction wasrefluxed for 1 hour, cooled to 0° C., and quenched by the carefuladdition of 2.7 mL of water, 2.7 mL of 15% aqueous sodium hydroxide, and8.1 mL of water. The resulting solids were removed by filtration and thefiltrate washed with water, brine, dried over magnesium sulfate,filtered and concentrated to afford 13.8 g of crude material, which wasrecrystallized from tetrahydrofuran and isooctane to afford 10.6 g of3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutylamine, mp 46°-49° C.,m/e=361 (M+H), which was contaminated by approximately 2% of3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutylamine.

Method 2

To 15.6 mL (60.4 mmol) of 70% sodium bis(methoxyethoxy)aluminum hydridein toluene, was added 15 mL of anhydrous toluene, and then after coolingto 0° C., a solution of 20.0 g (46 mmol) of the crude 95:5 mixture of3S-(N,N-dibenzyl)amino-2S-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether, and3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutyronitrile,O-trimethylsilyl ether from Example 28 in 10 mL of anhydrous toluene, ata rate so as to maintain the temperature below 15° C. After 2.5 hours atroom temperature, the reaction was quenched by the careful addition of200 mL of 5% aqueous sodium hydroxide. The solution was diluted withethyl acetate, washed with 5% sodium hydroxide, sodium tartratesolution, brine, dried over magnesium sulfate, filtered and concentratedto afford 16.6 g of crude product, which was assayed by HPLC and shownto contain 87% of 3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutylamine.

EXAMPLE 30 N-3S-(N,N-Dibenzyl)amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)urea

Step 1: To a solution of 1.0 g (2.77 mmol) of3S-(N,N-dibenzyl)amino-2R-hydroxy-4-phenylbutylamine from Example 29 in4.6 mL of ethanol, was added 0.3 mL (0.24 g, 2.77 mmol) ofisovaleraldehyde. After 1 hour at room temperature, the ethanol wasremoved under reduced pressure, 4 mL of ethyl acetate was added and thesolution purged with nitrogen. To the solution was added 360 mg of 5%platinum on carbon catalyst, the solution purged with 40 psig ofhydrogen and then maintained under 40 psig of hydrogen for 20 hours. Thesolution was purged with nitrogen, the catalyst removed by filtrationand the solvent removed under reduced pressure to afford 473 mg of thecrude product.

Step 2: The crude product from Step A was directly dissolved in 5.4 mLof ethyl acetate and 109 mg (1.1 mmol) of tertiary-butyl isocyanate wasadded. After 1 hour at room temperature, the solution was washed with 5%citric acid, brine, dried over magnesium sulfate, filtered andconcentrated to afford 470 mg of crude product. The crude product wasrecrystallized from ethyl acetate and isooctane to afford 160 mg of N-3S-(N,N-Dibenzyl)amino-2R-hydroxy-4-phenylbutyl!-N'-(1,1-dimethylethyl)-N-(3-methylbutyl)urea,mp 120.4°-121.7° C., m/e=530 (M+H).

From the foregoing detailed description, one skilled in the art caneasily ascertain the essential characteristics of this invention, andwithout departing from the spirit and scope thereof, can make variouschanges and modifications of the invention to adapt it to various usagesand conditions.

What is claimed is:
 1. A method of preparing a protected chiralalpha-amino alcohol of formula (II): ##STR21## wherein P¹ and P²independently are selected from the group consisting of acyl, aralkyl,alkenyl, silyl, araloxycarbonyl, alkoxycarbonyl andcycloakenylalkyl;wherein further P¹ and P² may be taken together withthe nitrogen atom of Formula II to form a heterocyclic ring systemcontaining said nitrogen atom as a ring member; and wherein R¹ isselected from the group consisting of alkyl, aryl, cycloalkyl,cycloalkylalkyl and arylalkyl, which are optionally substituted at oneor more substitutable positions with a moiety selected from the groupconsisting of alkyl, halo, NO₂, OR⁹ and SR⁹, wherein R⁹ is selected fromthe group consisting of hydrogen and alkyl; and wherein any of theforegoing groups P¹, P² and R¹ may be substituted with one or moreradicals independently selected from the group consisting of halo, alkylof C₁ -C₈, alkoxy, hydroxy, nitro, alkenyl, amino, alkylamino, acylaminoand acyl; or a pharmaceutically-acceptable salt thereof; said methodcomprising treating a corresponding aminoalcohol of said formula (II),wherein said P¹ and said P² are H, with an alkylating agents whereinsaid alkylating agent is added in a single step to react with saidaminoalcohol.
 2. The method of claim 1 wherein the aminoalcohol isL-phenylalaninol.
 3. The method of claim 1 further comprising selectingsaid P¹ to be the same as said P².
 4. The method of claim 1 furthercomprising selecting said P¹ and said P² independently from the groupconsisting of acyl, aralkyl, alkenyl, silyl, alkoxycarbonyl andcycloalkenylalkyl.
 5. The process of claim 3 further comprisingselecting said aminoalcohol to be L-phenylalanine.
 6. The process ofclaim 4 further comprising selecting said aminoalcohol to beL-phenylalanine.